Vertebral cage device with modular fixation

ABSTRACT

Intervertebral arthrodesis for insertion in an intervertebral space separating opposite faces of two adjacent vertebrae has a ring shaped intervertebral cage having a bar that extends perpendicular to the axis of the spine. The bar has a height less than the rest of the cage. A surface of the cage contacting the vertebrae has an undulating shape for limiting sliding of the cage in a plane parallel to the vertebrae faces.

The present invention concerns an arthrodesis device, used to enablefusing of two contiguous vertebrae by development of bony tissues withreplacement of fibrocartilaginous discs ensuring the bonding between thevertebrae of the vertebral column or the end of the latter.

The intervertebral discs are formed from a deformable but notcompressible part called “nucleus pulposus” containing approximately 80%water, surrounded by several elastic fibrous layers uniting to maintainthe nucleus, absorbing part of the forces applied to the disc unit, andstabilizing the articulation. These parts may often be degraded bycompression, displacement or wear and tear, following shocks,infections, exaggerated forces or simply over time. The degradation ofthis articulation part may cause intense pain in the patient andsignificant discomfort.

In a good number of cases, the treatment consists of removing all orpart of the damaged intervertebral disc and connecting the vertebraeconcerned by causing bony fusion between them. To do that, one placesbetween the vertebrae an artificial structure allowing their separationto be maintained, while with it introducing into the intervertebralspace either a bony graft or a bony substitute, compounded material thatwill be invaded by the growth of adjacent bony tissues. This structureoften takes the shape of an open or closed ring called cage, and may bepositioned on the basis of a cage by the intervertebral space in thecase of cervical vertebrae, or on the basis of one or two cages by theintervertebral space in the case of lumbar vertebrae. This positioningis done most often by the anterior surface of the vertebrae in the caseof a cervical cage, or by the anterolateral surface of the vertebrae(one cage) or posterior (two cages) of vertebrae in the case of a lumbarcage. As for grafts and bony substitutes, they are introduced in thecage either before or after its positioning and are therefore found incontact with the two vertebrae surrounding the treated intervertebralspace.

During the time necessary for growth and up to the reinforcement ofarthrodesis, which may be on the order of six months, it is importantthat the various movements of forces taking place in the intervertebralspace do not cause displacement of the cage, which would then riskdeteriorating the bony tissues during formation or even escaping outsidethis space and damaging the adjacent organs.

To avoid such displacements, a solution used consists of equipping thesurfaces of the cage in contact with the vertebrae with varieties ofshape such as saw tooth notches as described in the patents FR0006351 orFR2733413. Such a solution however proves to be insufficient in acertain number of cases.

Another solution consists of equipping the cage with a flange thatextends on the outside of the intervertebral space and is applied on theside of each of the two contiguous vertebrae, to which it is fixed by abone anchoring screw. Such a solution has been used since about 1988 andis described for example in the patent FR 2 747 034. Such a platehowever represents an overcrowding outside the intervertebral space thatsometimes may pose problems in particular in the case of arthrodesis ofthe cervical vertebrae where the space available is very limited. Infact, the presence of the plate may for example form a daily discomfortfor the patient or form an immediate or future obstacle in thepositioning of another cage with plate in one of the immediatelyadjacent plates.

Furthermore, in particular in the case of cervical vertebrae, themovements of the spine often have the tendency to cause loosening of thebone anchoring screws, which decreases the effectiveness of such a plateand may also cause damages to the organs surrounding the plate.

Therefore, it is worthwhile to also provide for a system enablingfixation of the cage without a part extending outside the intervertebralspace.

Moreover, these different solutions may fulfil the needs of anarthrodesis operation differently without it being necessarily possibleto know in advance which will be preferable. Therefore, it is easier andless expensive to provide for a modular device comprisinginterchangeable parts for achieving different solutions.

SUMMARY OF THE INVENTION

To remedy some of these drawbacks, the present invention proposes anintervertebral arthrodesis device designed to be inserted in anintervertebral space separating the opposite plates of the two adjacentvertebrae, characterised in that it comprises at least one structurecalled intervertebral cage presenting the shape of a ring that may ormay not be open, in which at least one part, along the axis of thespine, has a lower height than the rest of this same cage and forms asmall bar crossed by at least one drilling of the axis approximatelyperpendicular to the plate of at least one of the adjacent vertebrae.

According to one characteristic, the device includes at least oneintervertebral cage having on its surfaces in contact with thevertebrae, undulations in shape limiting its possibilities for slidingin a plane parallel to said vertebrae.

According to one characteristic, the device comprises at least onefixation structure for fixedly mounting the cage(s) to at least one ofthese vertebrae. The fixation structure can be added to at least oneintervertebral cage by insertion of a projecting part in at least onebore or opening of the cage.

According to one characteristic, the fixation structure includes atleast two bone anchoring pins with approximately parallel axes. The pinsare connected together by a small rod, and extend through openings orbores of the small rod of the cages. The pins extending through theopening are pushed into a face of at least one vertebra to keep the cagein position in the intervertebral space.

According to one characteristic, at least one of the bone anchoring pinsof the fixation structure includes reliefs for limiting thepossibilitites of the cage sliding outside the face where it isimpacted.

According to one characteristic, the fixation structure comprises atleast one fixation plate fixed to the external surface of at least onevertebra and including at least one opening or bore for receiving a boneanchoring screw fixed to this same vertebra.

According to one characteristic, at least one of the openings of thefixation plate presents in the plane of this plate a section at thelevel of its opening opposite the vertebra that is not as high as in itspart located within the thickness of the plate. A bone anchoring screwhas a head which presents at least one part of a section greater thanthat of the opening of the plate and is thus retained within this sameopening by this same external opening.

According to one feature the fixation structure includes at least twolocking studs with approximately parallel axes connected by a small rod.These locking studs are inserted into at least one hole or bore of atleast one intervertebral cage to lock said fixation structure to saidcage and to keep the cage in position in the intervertebral space.

According to one feature, at least one of the ends of the small rod hasat least one protuberance clipped in at least one housing arranged inthe wall of the intervertebral cage so as to limit or prevent themovements of this same rod relative to this same cage.

According to one characteristic, the fixation structure comprises afixation plate (called a hemiplate) coupled to the exterior surface ofat least one vertebra. The fixation plate structure includes at leastone opening or bore through which is inserted a bone anchoring screwfixed in other vertebra to keep said cage in position in theintervertebral space.

According to one feature, the fixation hemiplate with the small rodconnecting the anchoring pins or the locking studs forms a piece with an“L” section.

According to one characteristic, the fixation structure comprises afixation plate (called complete) coupled to the exterior surface of atleast two vertebra. Near each end of the plate there is at least onebore or opening through which is inserted a bone anchoring screw that isfixed in said vertebrae to prevent any migration of the intervertebralcage within or outside the intervertebral space.

According to one characteristic, the complete fixation plate with thesmall rod connects the anchoring pins or the locking studs with a “T”section.

According to one feature, the fixation plate includes an opening at thelevel of the intervertebral space. This opening enables the introductionor packing of a graft or bone substitute in the intervertebral spaceafter insertion of the device.

According to one characteristic, each bore in the fixation structureacts with a bone anchoring screw. When the anchoring screw is in place,it is located in a position shifted relative to a plane containing theaxis of the spine.

According to one feature, at least one intervertebral cage has, alongthe axis of the spine, a nonuniform height. This variation in heightinduces a determined angle between the vertebra faces with respect tothe adjacent vertebrae.

According to one characteristic, at least one of the constitutive partsof the device is made from a radiotransparent material.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, with its characteristics and advantages, will be moreclearly evident with the reading of the description made in reference tothe fixed drawings in which:

FIG. 1 a is a side sectional view of the device according to theinvention in an embodiment where the fixation device comprises anchoringpins and a top hemiplate;

FIG. lb is a side sectional view of the device according to theinvention in an embodiment where the fixation device comprises acomplete plate, with opening, added by locking studs and with anchoringscrews retained in the openings or bores of the plate;

FIG. 2 is a top sectional view of the device according to the inventionin an embodiment where the fixation device comprises anchoring pins anda low hemiplate;

FIG. 3 a is a perspective view of an intervertebral cage according to apreferred embodiment of the invention;

FIG. 3 b is a perspective view of a device according to a preferredembodiment of the invention before insertion of impacting pins in anembodiment where the fixation device comprises anchoring pins withundulations in shape;

FIG. 3 c is a perspective view of a device according to a preferredembodiment of the invention before impacting tongues in an embodiment,where the fixation device comprises anchoring tongues;

FIG. 4 a is a perspective view of a device according to a preferredembodiment of the invention where the fixation device comprisesanchoring pins and a low hemiplate;

FIG. 4 b is a perspective view of a device according to a preferredembodiment of the invention where the fixation device comprisesanchoring pins and a top hemiplate with an opening;

FIG. 5 a is a perspective view of a device according to a preferredembodiment of the invention where the fixation device comprisesanchoring pins and a complete plate with an opening; and

FIG. 5 b is a perspective view of a device according to a preferredembodiment of the invention where the fixation device comprises acomplete plate added by locking studs, illustrated with anchoringscrews.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is now made to the Figures wherein is illustrated ring shapedintervetrbral cage (1), designed to be inserted in the intervertebralspace (E) to be treated between two contiguous vertebrae, and to bereceived into an interior cavity (10, FIG. 2 a) a bony material actingas a graft, or any structure that can act as a bony substitute or be“assembled” by a growth of bony material. The cavity of theintervertebral cage can thus be filled before or after it is positionedin the intervertebral space.

According to some applications, the device includes a singleintervertebral cage (FIGS. 1 and 2 a), for example to carry outarthrodesis between two cervical vertebrae. It is to be understood thatfor other applications, the device can include two intervertebral cages(not represented), for example, to carry out arthrodesis between twolumbar vertebrae during postioning by the posterior route.

According to the applications, an intervertebral cage according to theinvention may be made in the shape of a closed ring (1, FIG. 3 a) or inthe form of a ring opened on one side (not represented).

In one embodiment represented in FIGS. 1 and 2 a, the inventioncomprises a fixation device enabling its anchoring in the plate (V0) ofa vertebra (V) within the intervertebral space (E) to be treated. Thisfixation device is formed from two anchoring pins (21, 22), withapproximately parallel axes and connected by a small rod (23). Theseanchoring pins are introduced into two drillings (121, 122) made in athinned down part of the intervertebral cage, then are impacted, that ispushed in with force, into the bony material forming the plate of one ofthe two vertebrae surrounding the intervertebral space to be treated.

In one embodiment, the thinned down part of the cage forms a small flatrod (12) that abuts small flat rod (23), connecting the two anchoringpins (21, 22) when the latter are impacted in face (V0) of a vertebra(V). The thickness of the small rod (23) connecting the anchoring pinsand the small rod (12) formed by a thinning of the intervertebral cage(1) are such that the superimposition of the two small rods (12, 23)after impacting is no higher along the axis of the spine than the restof the intervertebral cage (1).

In one embodiment represented in FIG. 3 b the length of the anchoringpins (21, 22) and the thickness of the small rod (23) connecting themare determined so that the sum of these two dimensions forming theheight of the fixation device in this embodiment is no greater than theheight along the axis of the spine of the rest of the intervertebralcage (1). Thus, it is possible to introduce into this intervertebralspace an intervertebral cage already provided with anchoring pins, thelatter then only having been impacted into the face (V0) of a vertebra(V), for example with the aid of a spreader, a distractor or anothertool of known type.

In one embodiment represented in FIG. 3 c, the fixation device, enablingthe device to be anchored in the face (V0) of a vertebra (V) within theintervertebral space (E) to be treated, is constituted of an anchoringtongue including legs (51, 52) having intersecting edges forming a “V”are connected by a small rod (53). Legs (51, 52) are introduced betweena thinned down part of the intervertebral cage formed by a small rod(62) and two lugs (only one, 54, is represented on FIG. 3 c) formed onthe device and symmetrically disposed in relation to the device axis.The “V” shaped anchoring tongue including legs (51, 52) is then forcedinto place similarly to the device provided with pins (21, 22). Legs(51, 52) are forced into place in face V0 of vertebra V so the smallflat rod (53), connecting the anchoring legs (51, 52), abuts small flatrod (62). The diameters of the small rod (53) connecting the anchoringtongues and the small rod (62) formed by a thinning of theintervertebral cage (1) are such that the superimposition of the twosmall rods (62, 53) after legs (51, 52) are forced into face (V0) is nohigher along the axis of the spine than the rest of the intervertebralcage (1).

In one embodiment (not shown), the device according to the inventioncomprises two intervertebral cages. Each of the two cages is formed froman open ring having at least one part having a reduced height along theaxis of the spinal cord. In one embodiment, at least one of the cages isin the shape of a “U” or “C” (not shown). Each cage includes at its enda small rod from one part having a reduced height along the axis of thespine. These small rods are crossed by at least one bore or openinghaving an axis approximately perpendicular to the face (V0) of thevertebra (V) with which they are in contact. In one embodiment, twointervertebral cages are arranged in the intervertebral space with theiropenings facing each other. At least one fixation device including twoanchoring pins with parallel axes connected by a small rod is introducedinto the bore of each of the two small rods with ends facing each other.The anchoring pins are then forced into the face of the vertebra andinserted into the bores of the small rods of the intervertebral cages tohelp to keep said cages immovable.

In one embodiment, an intervertebral cage (1) used in a device accordingto the invention has at least one undulating surface (11) in contactwith the vertebrae; in one example the undulating contact surface (11)has a saw tooth shape as illustrated in FIG. 3 c. Under the pressureexerted by the vertebrae surrounding the treated intervertebral space(E), the undulating surface (11) supports the surface of faces (V0) ofthese same vertebrae to limit the risks of displacement of theintervertebral cage.

In one embodiment, represented in FIGS. 1, 2 a and 4 b, a fixationdevice comprises a plate called top hemiplate (32), united with thesmall rod (23) connecting the anchoring pins (21, 22) to each other.Hemiplate (32) extends outside the intervertebral space (E) to betreated and is coupled to the exterior surface of the vertebra oppositethe vertebra receiving the anchoring pins. This top hemiplate (32)includes at least one bore or opening (321) which receives a boneanchoring screw (4) of a known type. Screw (4) is fixed in the body ofthe vertebra and inserted in the face(V0) to prevent any migration ofthe intervertebral cage (1) within or outside the treated intervertebralspace (E). Top hemiplate (32) also comprises an opening (320) enablingintroduction of the graft into the cage (1) after the cage is positionedin the intervertebral space. The part of the piece connecting the smallrod (23) and the top hemiplate (32) has an “L” shape.

In one embodiment represented in FIG. 4 a, a plate called bottomhemiplate (31), is fixed in the same way to the vertebra receiving theanchoring pins. The part of the piece connecting the small rod (23) andthe bottom hemiplate (31) has an “L” shape.

In one embodiment represented in FIG. 5 a, a fixation device comprises aplate called complete plate (33) that is integral with the small rod(23) connecting the anchoring pins (21, 22) to each other. Plate (33)extends to the exterior of the intervertebral space (E) to be treatedand is coupled to the exterior surface of these two vertebraesurrounding the intervertebral space (E) to be treated. The part of thepiece connecting the small rod (23) and the complete plate (33) has a“T” shape. Complete plate (33) includes at least two bores (331, 332),each of which receives a bone anchoring screw (4) of a known type. Screw(4) is fixed in the body of the corresponding vertebra and inserted inthe plate (33) to prevent any migration of the intervertebral cage (1)within or outside the treated intervertebral space (E). This completeplate (33) also comprises an opening (330) enabling introduction of thegraft into the cage (1) after the cage is placed in the intervertebralspace.

In one embodiment represented in FIGS. 1 b, 5 a and 5 b, a fixationdevice comprises a plate called complete plate (33) united with thesmall rod (23). Small rod (23) includes two locking studs (24, 25)perpendicular to the longitudinal axis of rod (23). Studs (24, 25) arehoused in the two bores (121, 122) of the intervertebral cage (1). Thiscomplete plate (33) extends outside the intervertebral space (E) to betreated and is coupled to the exterior surface of the two vertebraesurrounding the intervertebral space (E) to be treated. The use oflocking studs (24, 25) rather than pins makes it possible to use asofter material that is forced into the face of the vertebra, but on theother hand has the advantage of being transparent during radiography.The part of the piece connecting the small rod (23) and the completeplate (33) has a “T” shape in its section along a plane containing theaxis of the spine.

This complete plate (33) includes at least two bores (331, 332) each ofwhich receives a bone anchoring screw (4) of a known type. Screw (4) isfixed in the body of the corresponding vertebra and inserted into theface of the vertebra to prevent migration of the intervertebral cage (1)within or outside the treated intervertebral space (E).

In the embodiment illustrated in FIGS. 3 a and 5 a, each of the twoopposite ends of small rod (23) connecting the locking studs and thecomplete plate (33) has a rounded protuberance contacting the walls ofthe intervertebral cage (1). The rounded protuberances are clipped byelastic deformation in a housing (13) arranged in the wall opposite theintervertebral cage (1). The clipping of the protuberances (233) in thehousings (13) makes it possible to maintain the cage (1) and the plate(33) together during positioning of the unit or after positioning.

In one embodiment, to prevent the anchoring screws from loosening, forexample under the effect of the movements of the spine, the bores inplate (33) that receive the screws in a plane parallel to the plate (33)have a section slightly lower than the interior of the plate at thelevel of their opening on the surface opposite the vertebra; the surfaceopposite the vertebrae is called an external surface area. The heads ofthe screws have a part of a section greater than that of the externalopening of the bore. Thus, once the screw has been screwed to where thelarge part of the head of the screw has penetrated the interior of thebore under force, the elasticity of the material forming the plateretains the screw head within the bore, limiting the risks of laterloosening. This complete plate (33) also comprises an opening (330)enabling introduction of the graft into the cage (1) after positioningof the cage in the intervertebral space.

In one embodiment the plate (31, 32, 33) of the fixation device includesat least one bore (311, 321, 331, 332) for receiving a bone anchoringscrew (4) which is located in a position shifted relative to a planecontaining the axis of the spine. Thus, it is possible to treat twoadjacent intervertebral spaces by using fixation plates and bypositioning these plates in staggered rows. The shifted position of thebores in the plates enables the plates to be fixed in place by differentscrews located on the same vertebra and at the same height along theaxis of the spine.

In one embodiment, all or part of the device according to the inventionis made from a radiotransparent material, for example from PEEK, whichmakes it possible to monitor the development of bony tissues within thecage by radiography. In spite of that, for verification that theelements of the device are not displaced, it is possible to fix one ormore of the elements with a radio marker containing, for example, asmall piece of non-radiotransparent material.

Therefore, according to the applications it is possible to position anintervertebral cage (1) in different ways, simply by using one type oranother of fixation device. The same intervertebral cage (1) can, forexample, be positioned:

-   -   either alone,    -   or provided with a fixation device with pins (21, 22, 23),    -   or provided with a fixation device with pins and a top (32) or        bottom (33) hemiplate,    -   or provided with a fixation device with pins and with a complete        plate (33),    -   or provided with a top (32) or bottom (31) hemiplate added by        locking studs (24, 25),    -   or provided with a complete plate (33) added by locking studs        (24, 25).

Such modularity makes it possible for the surgeon to choose the type offixation during the surgery and according to the anatomic conditions heencounters, by having at his disposal a reduced number of componentsamong which to choose.

The fixation device that includes pins or a plate or both, can be laterremoved (for example during a new surgery) without significantdestruction of the arthrodesis. In fact, this device may no longer benecessary after reinforcement of the arthrodesis, although providingdiscomfort, either for the patient or for similar treatment of anadjacent intervertebral space.

It must be obvious for persons skilled in the art that the presentinvention makes possible embodiments under numerous other specific formswithout leaving the field of application of the invention as claimed. Asa result, the present embodiments must be considered as illustration,but may be modified in the field defined by the scope of the fixedclaims, and the invention must not be limited by the details givenabove.

1. Intervertebral arthrodesis device having a size and shape forinsertion in an intervertebral space separating opposite faces of twoadjacent vertebrae comprising at least one intervertebral cagesubstantially in the shape of a ring which may be open along a side andhaving a bar adapted to extend perpendicular to the axis of the spinewhen the arthrodesis device is inserted in the intervertebral space, thebar having a height less than another portion of the cage, and afixation structure for securing the at least one cage to at least one ofthe vertebrae, the fixation structure being arranged to be added to theat least one intervertebral cage by inserting a projecting part of thefixation structure through at least one opening extending along the bar,the fixation structure including at least two locking studs withapproximately parallel axes connected by a small rod, the locking studsbeing insertable into at least one opening of at least oneintervertebral cage to lock the fixation structure to the cage and tokeep the cage in position in the intervertebral space, and at least oneof the ends of the small rod has at least one protuberance clipped in atleast one housing arranged in the wall of the intervertebral cane forlimiting or preventing movements of said rod relative to said cage. 2.Device according to claim 1 wherein the ring is closed.
 3. Deviceaccording to claim 1 wherein the ring includes an open segment. 4.Device according to claim 1 wherein at least one intervertebral cageincludes on its surfaces adapted to contact the vertebrae an undulatingshape for limiting sliding of the cage in a plane parallel to the facesof said vertebrae.
 5. Device according to claim 1 wherein the fixationstructure comprises a fixation hemiplate coupled to the exterior surfaceof at least one vertebra, the fixation hemiplate including at least oneopening through which is inserted a bone anchoring screw for attachmentin said vertebra to keep said cage in position in the intervertebralspace.
 6. Device according to claim 1 wherein the fixation structurecomprises a complete fixation plate adapted to be coupled to theexterior surface of at least two vertebrae, the complete fixation plateincluding near each end at least one opening through each of which isadapted to be inserted into a bone anchoring screw adapted to be fixedin said vertebrae to prevent any migration of the intervertebral cagewithin or outside the intervertebral space.
 7. Device according to claim6 wherein the fixation plate includes an opening at the level of theintervertebral space, said opening enabling the introduction or packingof a graft or bony substitute in the intervertebral space afterinsertion of the device.
 8. Device according to claim 5 wherein each ofthe openings of the fixation structure acts together with a boneanchoring screw so that once in place the fixation structure is locatedin a position shifted relative to a plane containing the axis of thespine.
 9. Device according to claim 1 wherein the at least oneintervertebral cage has, along the axis of the spine, a non-uniformheight, the non-uniform height inducing a determined angle between thefaces of the vertebrae with respect to the adjacent vertebrae. 10.Device according to claim 1 wherein at least one of the constitutiveparts of the device is made from a radiotransparent material.